Ball Screw Position Correction via Tension Feedback
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Solution Overview
Problem
Existing servo control devices for converting rotational motion of a servo motor to linear motion through a ball screw face challenges in accurately correcting positioning errors due to factors like elastic deformation and thermal displacement, which affect the precision of the feed axis.
Innovation Solution
A servo control device that includes a position command generating unit, torque command generating unit, thermal displacement calculating unit, tension calculating unit, stretch/contraction calculating unit, and position correction unit, which together assess and correct for the thermal displacement and tension-induced stretch or contraction of the ball screw to improve positioning accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a ball screw is used to convert rotational motion to linear motion, then the feed axis can achieve motion conversion, but positioning errors occur due to elastic deformation and thermal displacement
Solution Approach 1:
The control device calculates the amount of stretch or contraction of the ball screw based on tension acting on it, and uses this information to correct positioning commands. This feedback mechanism compensates for elastic deformation and thermal displacement, resolving the contradiction between achieving motion conversion and maintaining positioning accuracy
Solution Approach 2:
The system dynamically adjusts positioning parameters by calculating tension-based stretch/contraction amounts and applying corrections to positioning commands. This parameter adjustment compensates for thermal and elastic effects, improving positioning accuracy while maintaining the ball screw's motion conversion function
2Productivity
If tension acts on the ball screw during operation, then the ball screw experiences stretch or contraction, but this causes positioning errors in the feed axis
Solution Approach 1:
The control device continuously calculates tension acting on the ball screw and determines the resulting stretch or contraction amount. This feedback is used to generate correction values that compensate for positioning errors, allowing the system to maintain both operational capability and positioning accuracy under tension
Solution Approach 2:
The system calculates and applies positioning corrections based on predicted tension effects before executing positioning commands. By preemptively compensating for expected stretch or contraction, the system maintains positioning accuracy during operation
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces positioning errors by calculating and correcting for the thermal displacement and tension effects on the ball screw, enhancing the precision of the feed axis movement.
Implementation Method 1
a thermal displacement amount calculating unit for calculating an amount of thermal displacement of the ball screw
Implementation Method 2
a stretch/contraction amount calculating unit for calculating an amount of stretch or contraction of the ball screw during operation of the servo motor, based on the tension calculated by the tension calculating unit
Data Source
AI summary
A servo control device in the present invention corrects a position command to a feed axis, so as to compensate for an amount of stretch or contraction of a ball screw during operation, by taking into account an influence of tension applied to the ball screw. The amount of stretch or contraction of the ball screw is calculated, based on the tension acting on the ball screw on the side farther from the servo motor, a distance between two fixed units supporting the ball screw at its opposite ends, a distance from the fixed unit situated closer to the servo motor to a moving body, and a torque command to the servo motor. An amount of position correction of the feed axis is calculated, based on the calculated amount of stretch or contraction of the ball screw.